1. Field of the Invention
The present invention relates to a gas turbine and a turbine rotor that uses vapor as a refrigerant for heating components.
2. Description of the Related Art
A technique for cooling heating components, such as a rotor blade, a rotor disk, or a stator blade in a gas turbine, by using vapor instead of air as a refrigerant, is now being used, in order to increase the thermal efficiency in the gas turbine. This is due to the following reasons. The specific heat at constant pressure of dry vapor is cp=1.86 kJ/kgK under a normal condition, which is a value almost twice as large as the specific heat at constant pressure of the air, wherein cp=1.00 kJ/kgK. Therefore, vapor has a large heat capacity and a high endothermic effect as compared with air of the same mass. Hence, when vapor is used as the refrigerant, the cooling efficiency can be increased as compared when using air, and the turbine inlet temperature of the combustion gas can be increased, thereby permitting an improvement in thermal efficiency.
In conventional air cooling, air from a compressor is used as a refrigerant for the rotor and stator blades of the turbine. However, when this compressed air is used for cooling, the work that can be obtained from the turbine decreases. If vapor is used instead of the air, the cooling air for the rotor and stator blades can be saved, and hence the work which can be recovered by the turbine increases by this amount, such that the work that can be obtained from the turbine can be increased.
FIG. 11 is a cross section view that shows a turbine rotor in a conventional gas turbine. In the gas turbine using vapor cooling, for a period of time after starting the gas turbine, the turbine rotor and stator blades and a rotor disk 250a are warned up or cooled by the compressed air generated by the compressor. This is because a certain period of time is required from the start-up of the gas turbine, in order to generate vapor sufficient for cooling these turbine rotor and stator blades and the rotor disk 250a by a heat recovery vapor generator (HRSG), using the exhaust gas from the gas turbine. When sufficient vapor is generated, the refrigerant is changed from the compressed air to the vapor.
The refrigerant for rotor disks 250a to 250d flows in such a manner that the refrigerant from a refrigerant supply pipe 225 for cooling the turbine rotor blade flows into a space between the rotor disks 250a and 250b, and then flows to spaces B, C, and D through a gap between a spindle bolt 260 and a bolt hole 262, to warm up or cool the rotor disks 250a to 250d. However, there is little convection of the refrigerant in spaces A to D, and hence time is required to warm up or cool the rotor disks 250a to 250d, thereby causing a problem in that the start-up of the gas turbine is delayed.
Further, the refrigerant flows from between the spindle bolt 260 and the bolt hole 262 in spaces A to D, but since the convection of the refrigerant in spaces A to D is of a small amount, the temperature only changes in the vicinity thereof, and the temperature change is slow. Therefore, a radial temperature distribution occurs in the rotor disks 250a to 250d. This transitional temperature distribution is not always uniform with respect to the circumferential direction, so as to cause temperature nonuniformity, and hence a thermal bend occurs in the turbine rotor 200. As a result, there is the possibility that the spindle vibrations of the rotor increase, to cause a trip (stoppage) of the gas turbine.